Interaction of E1 and hSNF5 proteins stimulates replication of human papillomavirus DNA

Mammalian viruses often use components of the host's cellular DNA replicati on machinery to carry out replication of their genomes, which enables these viruses to be used as tools for characterizing factors that are involved i n cellular DNA replication. The human papillomavirus (HPV) E1 protein is es sential for replication of the virus DNA(1-3). Here we identify the cellula r factor that participates in viral DNA replication by using a two-hybrid a ssay(4) in the yeast Saccharomyces cerevisiae and E1 protein as bait. Using this assay, we isolated Ini1/hSNF5 (ref. 5), a component of the SWI/SNF co mplex which facilitates transcription by altering the structure of chromati n(6). In vitro binding and immunoprecipitation confirmed that E1 interacts directly with Ini1/hSNF5. Transient DNA-replication assay revealed that HPV DNA replication is stimulated in a dose-dependent manner by addition of In i1/hSNF5, and that Ini1/hSNF5 antisense RNA blocks the replication of HPV D NA. Amino-acid substitution at residues that are conserved among E1 protein s prevented the E1-Ini1/hSNF5 interaction and reduced DNA replication of HP V in vivo. Our results indicate that Ini1/hSNF5 is required for the efficie nt replication of papillomavirus DNA and is therefore needed, either alone or in complex with SWI/SNF complex, for mammalian DNA replication as well.